My original heater-a/c fan was not blowing much air through the system. Just got the new motor and cage from specialtauto. Now it works great. Very satisfied with the results. If you haven't done this yet you will be impressed. I took my car out for a spin and had the a/c on and about froze my face off. Granted your system will work best if the gaskets in the heater control box are newer. The original ones are most likely have turned to goo after 30 some odd years.
I was skeptical at first but this product really worked for me.
Gary